Neonatal bacterial sepsis is a life threatening disorder occurring in approximately 1-10 patients per 1000 live term births and almost three to four times more commonly in preterm infants. The mortality rate for neonatal bacterial sepsis varies between 20 -75% depending on the organism, the immunocompetence of the host, and associated complications present at diagnosis. Nosocomial infections constitute a major cause of morbidity and mortality. Due to their immunologic immaturity, neonates are particularly vulnerable to the frequent invasive procedures and exposure to resistant organisms during their prolonged hospitalization. Reduced numbers of myeloid progenitor cells and circulating neutrophils contribute significantly to the developmental immaturity of neonatal host defense and to the increased susceptibility of the neonate to overwhelming infection. Future optimal therapy for prevention of neonatal nosocomial infection may include the use of adjuvant immunomodulator therapy. This study is attempting to define the role of recombinant human granulocyte-macrophage colony stimulating factor (rhu GM-CSF) as an immunomodulator of neonatal one marrow myeloid progenitor activity, its influence on circulating peripheral neutrophil counts and their functional activity, and whether this results in the prevention of neonatal nosocomial infection. Any significant reduction in the incidence of neonatal nosocomial infection will greatly reduce the number of hospital days required for preterm newborns and lessen the morbidity and mortality associated with this disorder.